(1) Field of the Invention
The invention relates to a method of metallization in the fabrication of integrated circuits, and more particularly, to a method of tungsten metallization resulting in improved step coverage and prevention of junction damage in the manufacture of integrated circuits.
(2) Description of the Prior Art
Conventional aluminum metallization suffers from bad step coverage, electromigration, and dog-bone problems. Tungsten-plug metallization can improve step coverage and alleviate electromigration concern since tungsten is a kind of refractory metal with high resistance to electromigration. However, overetching of the first metal layer results in considerable junction damage if the metal layer is designed without the dog-bone overlying the tungsten plug. FIG. 1A illustrates the dog-bone 1. Contact hole 2 is surrounded by the metal 3 in the shape of a dog-bone. Fig. 1B illustrates the contact hole 2 and metal 3 without the dog bone. The misalignment problem is overcome by using the dog-bone.
Referring now to FIG. 2, there is illustrated a conventional tungsten plug process of the prior art. There is shown semiconductor substrate 10 in which have been formed Field OXide (FOX) region 12 and source/drain regions 14. Gate electrode 18 has been formed overlying gate silicon oxide layer 16. A contact hole 22 has been opened through insulating layer 20 to source/drain region 14. Glue layer 24 has been deposited over the surface of the substrate and within the contact hole. Tungsten plug 26 has been formed within the contact hole.
Referring now to FIG. 3, second metallization 34 has been deposited. After metal etching, an overetch is required to overcome the nonuniformity problem and to remove residue that will cause stringers or shorts at some valley regions. The anisotropic overetch of metal layer 34 causes junction failure 36. A dog-bone shape 38 (shown in top view in FIG. 1A) would have prevented this spiking problem which causes junction failure. However, without the dog-bone, the metal line spacing can be designed to the minimum to shrink the chip size. It is desirable to avoid the spiking problem without using a dog-bone.
U.S. Pat. No. 5,216,282 to Cote et al shows the formation of a contact stud using a sidewall structure for alignment. They partially remove one sidewall layer and then replace it with a metal stud material.